This invention relates to a system for controlling cleaning equipment of a large scale boiler or other combustion device.
In the operation of large scale combustion devices, such as utility boilers, combustion products cause slag and ash encrustations to build on heat transfer surfaces, degrading the thermal performance of the system. In order to restore the thermal performance, various systems for cleaning the internal heat transfer surfaces are presently in use.
One type of cleaning system is referred to in the industry as sootblowers. Sootblowers are used to project a stream of a blowing medium, such as steam, air, or water, against heat exchanger surfaces within the combustion device. One type of sootblower is known as a long retracting type and incorporates a lance tube, which is periodically inserted into and withdrawn from the interior of the boiler. Nozzles at the distal end of the lance tube project a stream of the cleaning medium against the desired surfaces within the boiler.
Wall blower units are mounted to the outside wall of the boiler and project a stream of cleaning fluid through a wall port against surfaces within the boiler. Some of these devices use a lance which is not inserted into the boiler and is capable of articulating to aim its stream of fluid in a desired manner within the boiler interior.
Irrespective of the cleaning mechanisms used, it is necessary to control their operation so that they are not operated needlessly. The introduction of the steam, air, or water into the boiler for cleaning often has undesirable thermal efficiency effects. Moreover, their use for surfaces which do not need to be cleaned can cause physical damage to these interior boiler components. Accordingly, some mechanism is necessary to control the operation of boiler cleaning devices. A boiler may have dozens or more individually controlled sootblowers or other cleaning devices.
It is known to use various boiler operating parameters to activate the cleaning cycles of the boiler cleaning systems. One approach uses infrared cameras which evaluate the internal surfaces of the boiler. Since the walls which are coated with ash have a different reflectivity factor than other surfaces, this difference may be used as a means of measuring the development of slag and ash encrustations as an input for initiating a cleaning cycle. Heat flux sensors are also used which are placed within the heat transfer surfaces of the boiler and evaluate the difference in temperature between the wall surface and the process heat transfer fluid (typically water). A degradation in heat transfer is measurable as a difference in the temperature reading from these two thermocouples. Again, this output may be used as part of a boiler cleaning control system.
Boiler cleaning may also be initiated on a timed cycle, based on certain assumptions regarding the development of slag and ash encrustations over time.
Boiler cleaning systems which base their control decisions on the characteristics of selective surfaces do not comprehend the full impact of cleaning operation on the boiler plant operation.
From the above, it is seen that there exists a need for a cleaning system that controls the timing of the cleaning process to optimize the overall boiler efficiency.